Implementing reduced-protein diets for broiler chickens in emerging economies: supplementation with only the first three limiting amino acids

Abstract

This study evaluated the effects of reduced-protein diets supplemented with only the first three limiting amino acids (AAs); methionine, lysine, and threonine, on broiler performance, profitability, and nitrogen (N) utilization. Two hundred Cobb-500 broiler chicks were assigned to four dietary treatments in a Completely Randomized Design: a control diet and three reduced crude protein (CP) diets (-1PP, -2PP, -3PP). Diets contained CP levels of 21%, 20%, 19%, 18% during grower (14-28d) and 19.5%, 18.5%, 17.5%, 16.5% during finisher (28-42d) phases. Broilers on up to 2% CP reduction exhibited similar (P < 0.05) or superior growth performance and feed conversion ratio compared to 3% CP reduction. Gross margin was highest (P < 0.05) with up to 2% CP reduction but declined with further reduction. Carcass traits and breast yield decreased (P < 0.05) with CP reduction, though meat quality was unaffected. N intake and retention decreased (P < 0.05), while excretion and other N utilization parameters were unchanged. Nutrient digestibility remained consistent, but apparent metabolizable energy increased (P < 0.05) as dietary CP decreased. These findings indicate that reducing dietary CP by up to 2%, supplemented with the first three limiting amino acids, maintains growth performance, profitability, and meat quality. This approach also reduces environmental N emissions and offers a cost-effective strategy for developing economies compared to reduced-protein diets with additional amino acid supplementation.